linux-kernel - Re: [PATCH 03/12] s390: purgatory: pass --target option to clang

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Date:   Tue, 9 Apr 2019 09:30:49 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Philipp Rudo <prudo@...ux.ibm.com>,
        Hendrik Brueckner <brueckner@...ux.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/12] s390: purgatory: pass --target option to clang

On Tue, Apr 09, 2019 at 08:43:09AM +0200, Arnd Bergmann wrote:
> On Tue, Apr 9, 2019 at 12:03 AM Nathan Chancellor
> <natechancellor@...il.com> wrote:
> >
> > On Mon, Apr 08, 2019 at 11:26:16PM +0200, Arnd Bergmann wrote:
> > > The purgatory Makefile does not inherit the original cflags,
> > > so clang falls back to the default target architecture when
> > > building it, typically this would be x86 when cross-compiling.
> > >
> > > Pass --target=s390x-linux to all compilers that understand
> > > this option.
> > >
> > > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > > ---
> > >  arch/s390/purgatory/Makefile | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/arch/s390/purgatory/Makefile b/arch/s390/purgatory/Makefile
> > > index ce6a3f75065b..3a14b968cec3 100644
> > > --- a/arch/s390/purgatory/Makefile
> > > +++ b/arch/s390/purgatory/Makefile
> > > @@ -22,6 +22,7 @@ KBUILD_CFLAGS := -fno-strict-aliasing -Wall -Wstrict-prototypes
> > >  KBUILD_CFLAGS += -Wno-pointer-sign -Wno-sign-compare
> > >  KBUILD_CFLAGS += -fno-zero-initialized-in-bss -fno-builtin -ffreestanding
> > >  KBUILD_CFLAGS += -c -MD -Os -m64 -msoft-float -fno-common
> > > +KBUILD_CFLAGS += $(call cc-option,--target=s390x-linux)
> > >  KBUILD_CFLAGS += $(call cc-option,-fno-PIE)
> > >  KBUILD_AFLAGS := $(filter-out -DCC_USING_EXPOLINE,$(KBUILD_AFLAGS))
> > >
> > Would
> >
> > ifdef CONFIG_CC_IS_CLANG
> > KBUILD_CFLAGS += --target=s390x-linux
> > endif
> >
> > be a little clearer (and save a cc-option call)?
> 
> Fine with me as well. Actually I noticed later that we need the same
> thing for arch/s390/boot/Makefile and arch/s390/boot/compressed/Makefile
> in some form, so maybe we should drop this one for now and find
> a solution that works for all three of them. The boot stuff is the one
> patch I did not send, since I did not think I had a good solution there,
> just one that happened to make it build.
> 

It did just occur to me that we added the --target and --gcc-toolchain
flags to a clang specific variable, CLANG_FLAGS, that has already been
used by powerpc in commit 813af51f5d30 ("powerpc/boot: Set target when
cross-compiling for clang"). I assume that could be used here?

Nathan

> > Otherwise, makes sense.
> >
> > Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
> 
>  Thanks,
> 
>        Arnd